Modern computer processors and memory chips include millions of transistors that require gate currents to switch the transistors on and off to either store or retrieve data bits encoded by the transistors. Maintaining optimal switching speed requires that adequate charge supported by the appropriate voltage be available at all times. One or more centralized capacitor systems known as charge pumps (or charge pump generators) are utilized to supply the required charge, as needed, for switching millions of transistors on a particular chip or set of chips, such as a CPU or memory array. As the charge in the capacitor is drained by transistor switching, the voltage supplied by the capacitor begins to drop indicating the need to recharge the capacitor. The charge pump continually senses the capacitor voltage and periodically recharges the pump capacitor, as needed, to maintain the charge supply stored by the pump capacitor.
A water tower is a good analogy for the charge pump system, where the water stored in the tank is analogous to the electric charge stored in the pump capacitor. Transistor switching is analogous to use of the stored water by the community and the water pressure caused by the volume of water stored in the tank is analogous to the voltage. The flow of water at a local faucet is analogous to the gate current switching an individual transistor, where the state of a glass of water filled (and for this example also capable of being emptied) by the faucet might represent a data bit. The charge pump is analogous to the tank filling system, which continually monitors the water level or pressure in the tank and periodically refills the tank to ensure that an adequate supply of water remains in the tank.